Method and system for pre-ignition control

ABSTRACT

Methods and systems are provided for identifying and differentiating knock and pre-ignition using a plurality of knock sensors distributed along an engine block. By dynamically adjusting cylinder-specific assignment of the knock sensors for knock detection and pre-ignition detection based on operating conditions of each cylinder, knock and pre-ignition is more reliably identified and distinguished.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/960,218 filed Dec. 3, 2010, the entire contents of which areincorporated herein by reference for all purposes.

FIELD

The present description relates generally to methods and systems fordetecting pre-ignition in a vehicle engine.

BACKGROUND/SUMMARY

Under certain operating conditions, engines that have high compressionratios, or are boosted to increase specific output, may be prone to lowspeed pre-ignition combustion events. The early combustion due topre-ignition can cause very high in-cylinder pressures, and can resultin combustion pressure waves similar to combustion knock, but withlarger intensity. Such pre-ignition events can cause rapid enginedegradation. Accordingly, strategies have been developed for earlydetection of pre-ignition based on engine operating conditions.

One example approach is illustrated by Hashizume in U.S. Pat. No.5,632,247. Therein, pre-ignition and knock for a cylinder is detected bya knock sensor attached to the cylinder block. Specifically, based on anestimation of the knock sensor reading in two different timing windows,each with differing thresholds, pre-ignition is determined anddifferentiated from knock.

However, the inventors herein have identified potential issues with suchan approach. In one example, the sensitivity of the approach may varydepending on the positioning of the sensor. For example, the sensorlocation for reliably identifying knock in the cylinder may not alignwith the sensor location for reliably identifying pre-ignition in thecylinder. In another example, the presence of multiple sensors (oneknock sensor per cylinder) adds to component costs without necessarilyimproving the performance of either knock or pre-ignition detection inthe cylinder. As such, the reduced accuracy of engine pre-ignitiondetermination and differentiation (from knock) may lead to rapid enginedegradation.

Thus in one example, some of the above issues may be addressed by amethod of operating an engine including a plurality of knock sensorsdistributed on an engine block. In one embodiment, the method comprises,during engine operation, dynamically selecting a knock-indicating sensorfrom among the plurality of knock sensors for identifying knock in thecylinder, and dynamically selecting a pre-ignition-indicating sensorfrom among the plurality of knock sensors for identifying pre-ignitionin the cylinder, the selections based on operating conditions.

In one example, a vehicle engine may include a first and a second knocksensor distributed at different positions along the engine block. Duringa first condition (such as based on the engine speed-load conditions,cylinder position, and cylinder firing order), knock and pre-ignitionmay be identified in a first cylinder based on the first knock sensorwhile knock and pre-ignition is identified in a second cylinder based onthe second knock sensor. In comparison, during a second condition, knockand pre-ignition may be identified in the first cylinder based on thesecond knock sensor while knock and pre-ignition is identified in thesecond cylinder based on the first knock sensor. In this way, byassigning different knock sensors to each cylinder based on engineoperating conditions, the knock and pre-ignition detection sensitivityfor each cylinder can be improved with fewer knock sensors.

In another example, during a first condition, cylinder knock (in anygiven cylinder) may be identified based on the first knock sensor whilecylinder pre-ignition is identified based on the second knock sensor.During a second condition, cylinder knock in the given cylinder may beidentified based on the second knock sensor while cylinder pre-ignitionis identified based on the first knock sensor. During still otherconditions, each of knock and pre-ignition in the given cylinder may beidentified based on the first or the second sensor.

It will be appreciated that while the above-mentioned examplesillustrate the concept using two knock sensors and two cylinders, thisis not meant to be limiting. As such, for a given cylinder, knock orpre-ignition may be identified based on one or more of a plurality ofknock sensors distributed along the engine block. Therein, the one ormore knock-indicating sensors may or may not overlap with the one ormore pre-ignition-indicating sensors.

In this way, by improving the sensitivity of cylinder knock andpre-ignition detection, abnormal cylinder combustion events may beidentified more accurately. By enhancing the differentiation of cylinderknock events from cylinder pre-ignition events, appropriate mitigatingsteps can be taken. By improving the accuracy and response time ofpre-ignition detection and mitigation, engine degradation due topre-ignition can be reduced. By improving the accuracy and response timeof knock detection, fuel economy benefits may be achieved. Further, byusing the same knock sensor to identify both knock and pre-ignition ineach cylinder, synergistic benefits may be achieved.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example engine system with a plurality of knock sensors.

FIG. 2 shows an example combustion chamber.

FIG. 3 shows a high level flow chart for selecting a knock-indicatingsensor and a pre-ignition indication sensor, from among a plurality ofknock sensors, for identifying knock and pre-ignition in each cylinderof the engine of FIG. 1.

FIGS. 4-6 show tables with example sensor combinations for cylinderknock and pre-ignition detection.

FIG. 7 shows an example of knock and pre-ignition differentiation in anengine cylinder, based on the output of one or more knock sensors,according to the present disclosure.

DETAILED DESCRIPTION

The following description relates to systems and methods for identifyingand differentiating cylinder knock and pre-ignition using a plurality ofknock sensors distributed along an engine block, as shown in the enginesystem of FIG. 1. As elaborated herein with reference to FIG. 3, anengine controller may dynamically select one or more knock-indicatingsensors and one or more pre-ignition-indicating sensors from among theplurality of knock sensors for identifying knock and pre-ignition ineach cylinder. The selection may be performed for each cylinder based onthe operating conditions of the given cylinder (such as, enginespeed-load conditions, the firing order of the cylinder, etc.). Examplesensor combinations are illustrated in the tables of FIGS. 4-6. Bydynamically adjusting the sensor combination used for each cylinderbased on operating conditions, both knock and pre-ignition detectionsensitivity for each cylinder may be improved. As shown in FIG. 7, byassessing the output of the selected knock sensor(s) in different timingwindows, and with regards to different thresholds, pre-ignition eventsmay be more reliably differentiated from knocking events. By improvingthe accuracy of knock and pre-ignition detection and differentiation,appropriate mitigating actions can be rapidly executed, thereby reducingengine degradation due to abnormal combustion events.

FIG. 1 shows a schematic depiction of a vehicle system 6 including anengine system 8. The engine system 8 may include an engine 10 having aplurality of cylinders 30. Engine 10 includes an engine intake 23 and anengine exhaust 25. Engine intake 23 includes a throttle 62 fluidlycoupled to the engine intake manifold 44 via an intake passage 42. Theengine exhaust 25 includes an exhaust manifold 48 eventually leading toan exhaust passage 35 that routes exhaust gas to the atmosphere.Throttle 62 may be located in intake passage 42 downstream of a boostingdevice, such as turbocharger 50, or a supercharger, and upstream of anafter-cooler (not shown). As such, the after-cooler may be configured toreduce the temperature of the intake air compressed by the boostingdevice. Turbocharger 50 may include a compressor 52, arranged betweenintake passage 42 and intake manifold 44. Compressor 52 may be at leastpartially powered by exhaust turbine 54, arranged between exhaustmanifold 48 and exhaust passage 35, via turbine shaft 56.

Engine exhaust 25 may include one or more emission control devices 70,which may be mounted in a close-coupled position in the exhaust. One ormore emission control devices may include a three-way catalyst, lean NOxfilter, SCR catalyst, PM filter, etc.

Engine system 8 may further include a plurality of knock sensorsdistributed along engine block 11. In the depicted example, enginesystem 8 is shown with a first knock sensor 90 located at one end of thecylinder block and a second knock sensor 92 located (symmetrically) atthe other end of the cylinder block. However, it will be appreciatedthat in alternate embodiments, a larger number of knock sensors may beincluded. Further, the knock sensors may be distributed symmetrically orasymmetrically along the engine block.

As elaborated in FIG. 3, an engine controller may be configured toselect one or more of knock sensors 90, 92 for indicating knock andpre-ignition in each cylinder, the selection based on engine operatingconditions. By positioning the knock sensors are different locationswithin the engine block, and dynamically adjusting the selection ofsensors during engine combustion, an improved signal to noise ratio fordetecting both pre-ignition and knock in each of the engine cylindersmay be achieved.

The engine controller may also be configured to differentiate abnormalcombustion events due to cylinder knocking from those indicative ofcylinder pre-ignition based on the selected knock sensors. As such,knock sensors 90, 92 may be an accelerometer, or an ionization sensor.As elaborated in FIGS. 3 and 7, based on the output of the selectedknock sensor, such as based on a signal timing, amplitude, intensity,frequency, etc., the controller may differentiate knock frompre-ignition. In one example, a cylinder pre-ignition event may bedetermined based on a cylinder knock signal estimated in a first,earlier window being larger than a first, higher threshold, while acylinder knock event may be determined based on a cylinder knock signalestimated in a second, later window being larger than a second, lowerthreshold. In one example, the windows in which the knock signals areestimated may be crank angle windows.

Mitigating actions taken by the engine controller to address knock mayalso differ from those taken by the controller to address pre-ignition.For example, knock may be addressed using ignition spark timingadjustments (e.g., spark retard) and EGR, while pre-ignition may beaddressed using load-limiting and fuel enrichment.

The vehicle system 6 may further include control system 14. Controlsystem 14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein) and sending controlsignals to a plurality of actuators 81 (various examples of which aredescribed herein). As one example, sensors 16 may include exhaust gassensor 126 (located in exhaust manifold 48), knock sensors 90 and 92,temperature sensor 128, and pressure sensor 129 (located downstream ofemission control device 70). Other sensors such as pressure,temperature, air/fuel ratio, and composition sensors may be coupled tovarious locations in the vehicle system 6, as discussed in more detailherein. As another example, the actuators may include fuel injectors 66,and throttle 62. The control system 14 may include a controller 12. Thecontroller may receive input data from the various sensors, process theinput data, and trigger the actuators in response to the processed inputdata based on instruction or code programmed therein corresponding toone or more routines. An example control routine is described hereinwith reference to FIG. 3.

FIG. 2 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10 (of FIG. 1). Engine 10 may receivecontrol parameters from a control system including controller 12 andinput from a vehicle operator 130 via an input device 132. In thisexample, input device 132 includes an accelerator pedal and a pedalposition sensor 134 for generating a proportional pedal position signalPP. Cylinder (herein also “combustion chamber’) 30 of engine 10 mayinclude combustion chamber walls 136 with piston 138 positioned therein.Piston 138 may be coupled to crankshaft 140 so that reciprocating motionof the piston is translated into rotational motion of the crankshaft.Crankshaft 140 may be coupled to at least one drive wheel of thepassenger vehicle via a transmission system. Further, a starter motormay be coupled to crankshaft 140 via a flywheel to enable a startingoperation of engine 10.

Cylinder 30 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 30. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 2 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 20 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 20 may be disposed downstream ofcompressor 174 as shown in FIG. 2, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 30. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 128. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods listedherein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 30 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 30. In some embodiments, eachcylinder of engine 10, including cylinder 30, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The position ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors 155 and 157, respectively. In alternative embodiments,the intake and/or exhaust valve may be controlled by electric valveactuation. For example, cylinder 30 may alternatively include an intakevalve controlled via electric valve actuation and an exhaust valvecontrolled via cam actuation including CPS and/or VCT systems. In stillother embodiments, the intake and exhaust valves may be controlled by acommon valve actuator or actuation system, or a variable valve timingactuator or actuation system.

Cylinder 30 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 30 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 30 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 30 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 30. While FIG. 2shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 166 from a high pressure fuel system 8 including fueltanks, fuel pumps, and a fuel rail. Alternatively, fuel may be deliveredby a single stage fuel pump at lower pressure, in which case the timingof the direct fuel injection may be more limited during the compressionstroke than if a high pressure fuel system is used. Further, while notshown, the fuel tanks may have a pressure transducer providing a signalto controller 12. It will be appreciated that, in an alternateembodiment, injector 166 may be a port injector providing fuel into theintake port upstream of cylinder 30.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel tanks in fuel system 8 may hold fuel with different fuel qualities,such as different fuel compositions. These differences may includedifferent alcohol content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; absolute manifold pressure signal (MAP) from sensor124, cylinder AFR from EGO sensor 128, and abnormal combustion from aknock sensor and a crankshaft acceleration sensor. Engine speed signal,RPM, may be generated by controller 12 from signal PIP. Manifoldpressure signal MAP from a manifold pressure sensor may be used toprovide an indication of vacuum, or pressure, in the intake manifold.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

Now turning to FIG. 3, an example routine 300 is described for selectingone or more knock sensors from a plurality of knock sensors to determineknock and pre-ignition in each cylinder based on operating conditions.By dynamically adjusting the selection of knock sensors during engineoperation based on real-time operating conditions of each cylinder, theaccuracy and speed of detection and differentiation of abnormalcombustion events in each cylinder of the engine can be improved.

At 302, engine operating conditions may be estimated and/or measured.The operating conditions determined may include, for example, enginespeed, torque, engine load, engine temperature, engine manifoldpressure, air temperature, etc. Cylinder-specific conditions for eachcylinder may also be determined, such as cylinder pressure (IMEP),cylinder temperature, cylinder air charge, etc. At 304, one or moreknock-indicating sensors may be dynamically selected from among theplurality of knock sensors on the engine block for identifying knock ineach cylinder based on the estimated operating conditions. Additionally,one or more pre-ignition-indicating sensors may be dynamically selectedfrom among the plurality of knock sensors on the engine block foridentifying pre-ignition in the cylinder based on the estimatedoperating conditions.

As elaborated herein with reference to the tables of FIGS. 4-5, duringsome conditions a single sensor may be selected for indicating knock andpre-ignition in a given cylinder. Herein, in one example, theknock-indicating sensor may be same as the pre-ignition indicatingsensor, while in an alternate example, the knock-indicating sensor maybe different from the pre-ignition indicating sensor. During otherconditions, as elaborated in the table of FIG. 6, a plurality ofknock-indicating sensors may be selected from among the plurality ofknock sensors for indicating cylinder knock and/or a plurality ofpre-ignition-indicating sensors may be selected from among the pluralityof knock sensors for indicating cylinder pre-ignition. Therein, in oneexample, at least one of the knock-indicating sensors may be the same asat least one of the pre-ignition indicating sensors, while in analternate example, each of the plurality of knock-indicating sensors maybe different from each of the plurality of pre-ignition indicatingsensors.

The selections may be pre-mapped and stored in a look-up table (forexample, in a speed-load based map) in the controller's memory, andaccessed by the controller during engine operation and cylindercombustion. In some embodiments, during mapping, one or more knocksensors may be selected for a cylinder based on the respectivecylinder's operating conditions taking into consideration other cylinderdetails, such as the cylinder's location on the engine block, thecylinder's firing order, etc. For example, under otherwise identicalengine operating conditions, the selection may vary based on whether thecylinder is in an in-line engine, or whether the cylinder is on a V-typeengine (and further, which bank therein). Similarly, under otherwiseidentical engine operating conditions, the selection may vary based onthe firing order of the cylinder.

In another example, the sensor selections may be dynamically determined(e.g., in real-time) during engine operation and cylinder combustion.For example, the dynamic selection may be repeated at fixed intervals(e.g., after a defined amount of time, or after a defined number ofcombustion events). Alternatively, the dynamic selection may be repeatedin response to a change in engine speed and/or load (e.g., in responseto a threshold change in speed or load). By adjusting the sensorselection primarily and dynamically in response to engine operatingconditions, and not based on other factors (such as, acoustic signals),the accuracy of knock and pre-ignition detection can be maintained undersubstantially all engine operating conditions, and at any given pointduring engine operation, knock and pre-ignition can be reliablydifferentiated.

At 306, for each cylinder, a knock window may be determined for theknock-indicating sensor(s) and a pre-ignition window may be determinedfor the pre-ignition indicating sensor(s), based on the estimatedoperating conditions. The knock window may be a first, later windowwhile the pre-ignition window may be a second, earlier window. In oneexample, the knock window and the pre-ignition window may be completelydistinct, with no overlap. In another example, the first knock windowmay partially overlap with the second pre-ignition window. In stillanother example, the first and second windows may fully overlap (forexample, one window within the other window). In one embodiment, theknock window and pre-ignition window may be crank angle timing windows.However, other timing windows may also be possible. By estimating theoutput of the selected sensors in distinct windows, abnormal combustionevents related to cylinder knock may be more reliably differentiatedfrom abnormal combustion events related to pre-ignition. Additionally,knock and pre-ignition thresholds for the respective windows may also bedetermined based on the estimated operating conditions.

In one example, the knock and pre-ignition detection windows andthresholds may be selected based on the sensor selections. For example,for a given cylinder, the knock detection window (and threshold) may bebased on the knock-indicating sensor selected while the pre-ignitiondetection window (and threshold) is based on the pre-ignition indicatingsensor selected. In another example, knock and pre-ignition detectionwindows may be determined for each cylinder and sensor selections may bebased on, or adjusted based on, the window selection. For example, aselaborated herein, during some conditions, the knock or pre-ignitionwindow may be broadened, and the sensor selection may be adjusted basedon the broadened window (e.g., the number of sensors used for indicatingknock or pre-ignition may be increased in the broadened window). Instill other examples, the knock and pre-ignition detection windows (andthresholds) may be determined independent of the selection ofknock-indicating sensors and pre-ignition-indicating sensors.

At 308, the output of the knock-indicating sensor may be estimated inthe first, later window and it may be determined whether the outputexceeds a first (lower) threshold (“knock_threshold”). If no, then at310, no cylinder knock is determined and the routine may end. Incomparison, if the knock-indicating sensor output exceeds the firstthreshold, the routine may proceed to 312 wherein the output of thepre-ignition-indicating sensor may be estimated in the second, earlierwindow and it may be determined whether the output exceeds a second(higher) threshold (“preignition_threshold”).

If the pre-ignition-indicating sensor output exceeds the secondthreshold at 312, then at 318, cylinder pre-ignition may be indicatedand at 320, pre-ignition mitigating operations may be executed.Indicating cylinder pre-ignition may include setting a diagnostic codeand updating a cylinder pre-ignition count in the database.Additionally, an engine pre-ignition count may be updated. Incomparison, if the pre-ignition-indicating sensor output does not exceedthe threshold, then at 314, cylinder knock may be indicated in responseto the knock-indicating sensor output exceeding the threshold, and at316, knock mitigating operations may be executed. Indicating cylinderknock may include setting an alternate diagnostic code.

Knock-detection windows and threshold may also be predetermined andstored in the look-up table along with, and based on, the sensorselections. An example of differing windows and thresholds of a firstand second knock sensor used to identify and differentiate knock andpre-ignition in a first and second cylinder is elaborated herein withreference to FIG. 7.

As such, the mitigating operations used to address cylinder knock may bedifferent from those used to address cylinder pre-ignition. For example,in response to the indication of cylinder knock, an engine controllermay retard ignition spark timing of the affected cylinder. Incomparison, in response to the indication of cylinder pre-ignition thecontroller may enrich fuel injection to the affected cylinder and/orbank of cylinders. The enrichment may be adjusted based on the affectedcylinder's pre-ignition count. For example, a degree of enrichmentand/or duration of enrichment may be increased as the cylinderpre-ignition count increases. In some embodiments, in addition to theenrichment, a cylinder load may be limited, for example, by adjusting acam timing of the affected cylinder (or bank of cylinders) to limit anamount of air charge directed to the cylinder (or bank).

In this way, by adjusting the selection of sensors based on engineoperating conditions, as well as the knock and pre-ignition detectionwindows and thresholds for the sensors based on the sensor selection,knock and pre-ignition may be rapidly identified and addressed. As such,this may reduce rapid engine degradation due to pre-ignition.

Now turning to FIG. 4, a table 400 is illustrated that depicts exampleknock sensor selections for a cylinder in an engine that includes afirst and a second knock sensor located at different locations along theengine block. By dynamically adjusting the knock sensor selected foridentifying knock and pre-ignition in the cylinder based on engineoperating conditions, knock and pre-ignition detection performance forthe cylinder can be improved.

In one example, during a first condition, knock and/or pre-ignition maybe indicated in the cylinder based on one of the first and second knocksensor, and then during a second condition, knock and/or pre-ignitionmay be indicated based on the other of the first and second knocksensor. For example, during a first, low speed-low load condition,cylinder knock may be indicated based on the first knock sensor whilecylinder pre-ignition may be indicated based on the second knock sensor.In comparison, during a second, high speed-high load condition, knockmay be indicated in the cylinder based on the second knock sensor whilepre-ignition in the cylinder is indicated based on the first knocksensor. In another example, during a low speed-high load condition, eachof knock and pre-ignition may be indicated in the cylinder based on thefirst knock sensor while during a high speed-low load condition, each ofknock and pre-ignition in the cylinder may be indicated based on thesecond knock sensor.

In this way, by using the same sensor for detecting knock in a cylinderunder some conditions, and detecting pre-ignition in the same cylinderunder other conditions, the detection sensitivity and reliability forboth knock and pre-ignition detection can be improved without the needfor additional sensors.

While the above-mentioned conditions depict selecting a single sensorfrom among the first and the second knock sensor, during still otherconditions, each of the first and second knock sensor may be selected.For example, during a first condition, knock may be indicated in thecylinder based on one of the first or second knock sensor whileindicating pre-ignition in the cylinder based on each of the first andsecond knock sensor. In comparison, during a second condition, knock maybe indicated in the cylinder based on each of the first and second knocksensor while indicating pre-ignition in the cylinder based on one of thefirst and second knock sensor.

With reference to the examples depicted table 400, during a first highspeed-medium load condition, cylinder knock may be indicated based onthe first knock sensor while pre-ignition is indicated based on each ofthe first and second knock sensor, and during a low speed-medium loadcondition, cylinder knock may be indicated based on the second knocksensor while pre-ignition is indicated based on each of the first andsecond knock sensor. In comparison, during a medium speed-high loadcondition, cylinder knock may be indicated based on the first and secondknock sensor while pre-ignition may be indicated based on the firstknock sensor. Similarly, during a medium speed-low load condition,cylinder knock may be indicated based on the first and second knocksensor while pre-ignition is indicated based on the second knock sensor.In still further examples, a plurality of sensors may be selected todetect each of knock and pre-ignition in the cylinder, as illustrated intable 400 in the example of medium speed-medium load conditions.

It will be appreciated that while the depicted example is illustratedfor making a selection for a cylinder from among two knock sensors, thisis not meant to be limiting, and that the selection may be similarlymade for the given cylinder from among a plurality of sensorsdistributed at different locations along the engine block.

Now turning to FIG. 5, table 500 depicts example sensor selections for afirst and a second cylinder of an engine that includes a first and asecond knock sensor located at different locations along the engineblock. By dynamically adjusting the knock sensor selected foridentifying knock and pre-ignition in each cylinder from among the knocksensors present based on engine operating conditions, knock andpre-ignition detection sensitivity for each cylinder may be improvedusing the existing number of knock sensors.

In some embodiments, only one knock sensor may be selected from amongthe available knock sensors for identifying knock or pre-ignition ineach cylinder. In one example, as shown in table 500, during a firstcondition (condition 1), knock may be indicated in the first cylinderbased on the first knock sensor and pre-ignition may be indicated in thesame cylinder based on the second knock sensor. At the same time, knockmay be indicated in the second cylinder based on the second knock sensorand pre-ignition may be indicated in the same cylinder based on thefirst knock sensor. In another example, during a second condition(condition 2), knock may be indicated in the first cylinder based on thesecond knock sensor and pre-ignition may be indicated in the samecylinder based on the first knock sensor, while knock is indicated inthe second cylinder based on the first knock sensor and pre-ignition isindicated in the same cylinder based on the second knock sensor. In thisway, by using mutually exclusive knock sensors (or sensor combinations)for identifying knock or pre-ignition in the two cylinders, thedetection range of each sensor can be widened without reducing detectionsensitivity.

In another example (condition 3), knock may be indicated in each of afirst and second cylinder based on the first knock sensor whilepre-ignition is indicated in each of the first and second cylinder basedon the second knock sensor. During an alternate condition (condition 4),knock may be indicated in each of the first and second cylinder based onthe second knock sensor while pre-ignition is indicated in each of thefirst and second cylinder based on the first knock sensor.

In another example (condition 5), each of knock and pre-ignition may beindicated in the first cylinder based on the first knock sensor whileeach of knock and pre-ignition is indicated in the second cylinder basedon the second knock sensor. During an alternate condition (condition 6),each of knock and pre-ignition may be indicated in the first cylinderbased on the second knock sensor while each of knock and pre-ignition isindicated in the second cylinder based on the first knock sensor.

During some operating conditions, even though a plurality of knocksensors are available, a single sensor may be ideally positioned toidentify both knock and pre-ignition in each of the cylinders. Based onthe operating conditions, the single sensor selected for identifyingknock and pre-ignition in all the cylinders may be dynamically varied.For example, during a first (condition 7), each of knock andpre-ignition may be indicated in each of the first and second cylinderbased on the first knock sensor while during an alternate condition(condition 8), each of knock and pre-ignition may be indicated in eachof the first and second cylinder based on the second knock sensor. Inone example, during such conditions, the knock and pre-ignitionthresholds for each cylinder may be varied, even though the same sensoris used for detecting knock and pre-ignition in the cylinders.

During still other operating conditions, a common knock sensor may beused to indicate knock in each of the cylinders, while different (e.g.,mutually exclusive) knock sensors are used to indicate pre-ignition ineach of the cylinders. In one example (conditions 9 and 10), knock maybe indicated in each of the first and second cylinders based on thefirst knock sensor while pre-ignition is indicated in the first cylinderbased on one of the first and second cylinder, and pre-ignition isindicated in the second cylinder based on the other of the first andsecond cylinder. In another example (conditions 11 and 12), knock may beindicated in each of the first and second cylinders based on the secondknock sensor while pre-ignition is indicated in the first cylinder basedon one of the first and second cylinder, and pre-ignition is indicatedin the second cylinder based on the other of the first and secondcylinder.

In the same way, during other operating conditions, a common knocksensor may be used to indicate pre-ignition in each of the cylinders,while different (e.g., mutually exclusive) knock sensors are used toindicate knock in each of the cylinders. In one example (conditions 13and 14), pre-ignition may be indicated in each of the first and secondcylinders based on the first knock sensor while knock is indicated inthe first cylinder based on one of the first and second cylinder, andknock is indicated in the second cylinder based on the other of thefirst and second cylinder. In another example (conditions 15 and 16),pre-ignition may be indicated in each of the first and second cylindersbased on the second knock sensor while knock is indicated in the firstcylinder based on one of the first and second cylinder, and knock isindicated in the second cylinder based on the other of the first andsecond cylinder.

It will be appreciated that while the examples depicted in table 500illustrate selecting a single knock sensor for each of the two cylindersfrom among two knock sensors, this is not meant to be limiting, and thatin further examples, a single knock sensor may be selected from among aplurality of knock sensors (such as, three or more knock sensors). Itwill also be appreciated that while the depicted examples illustratesensor selections for two cylinders, the selection may be similarly madefor a plurality of cylinders (that is, from cylinder 1 through cylindern in an engine with n cylinders). In one example, the selections may bepre-mapped and stored in a look-up table (for example, in a speed-loadbased map) in the controller's memory. The look-up table may be accessedby the controller based on changes in engine operating conditions toadjust the sensor selection. In another example, the sensor selectionsmay be dynamically determined and adjusted during engine operation andcylinder combustion. In this way, the selection of knock sensors used toindicate knock and pre-ignition in each of the cylinders may be rapidlyand dynamically changed based on operating conditions so that at anygiven point during engine operation, knock and pre-ignition can bereliably identified for all the cylinders of the engine.

Now turning to FIG. 6, table 600 depicts example sensor selections for afirst and a second cylinder of an engine that includes a plurality ofknock sensors (such as, a first and a second knock sensor) located atdifferent locations along the engine block. Specifically herein, aplurality of knock-indicating sensors and/or a plurality ofpre-ignition-indicating sensors may be selected from among the pluralityof knock sensors. By using a plurality of knock sensors for identifyingknock or pre-ignition during some conditions, while using a single knocksensor for identifying knock or pre-ignition during other conditions,pre-ignition detection and differentiation from knock may be enhanced ineach of the cylinders without the need for dedicated sensors in eachcylinder.

During some conditions, an engine controller may dynamically select aplurality of knock-indicating sensors from among the plurality ofsensors for identifying knock in the cylinder while dynamicallyselecting a (single) pre-ignition-indicating sensor from among theplurality of sensors for identifying pre-ignition. Herein, one of theplurality of knock-indicating sensors may be the same as thepre-ignition-indicating sensor. Alternatively, each of the plurality ofknock-indicating sensors may be different from thepre-ignition-indicating sensor.

In one example, as shown in table 600, during some conditions(conditions 1-8), knock may be indicated in the first cylinder based onthe first and second knock sensor, and pre-ignition may be indicated inthe first cylinder based on either the first or the second knock sensor,while knock and pre-ignition is indicated in the second cylinder basedon either the first or the second knock sensor. In another example,during other conditions (conditions 17-24), knock may be indicated inthe second cylinder based on the first and second knock sensor, andpre-ignition may be indicated in the second cylinder based on either thefirst or the second knock sensor, while knock and pre-ignition isindicated in the first cylinder based on either the first or the secondknock sensor. In still another example, during some conditions(conditions 37-40), knock may be indicated in each of the first andsecond cylinder based on the first and second knock sensors whilepre-ignition is indicated in each of the first and the second cylinderbased on either the first or the second knock sensor.

During other conditions, the engine controller may dynamically select aplurality of pre-ignition-indicating sensors from among the plurality ofsensors for identifying pre-ignition in the cylinder while dynamicallyselecting a (single) knock-indicating sensor from among the plurality ofsensors for identifying knock. Herein, one of the plurality ofpre-ignition-indicating sensors may be the same as the knock-indicatingsensor. Alternatively, each of the plurality of pre-ignition-indicatingsensors may be different from the knock-indicating sensor.

For example, during some conditions (conditions 9-16), pre-ignition maybe indicated in the first cylinder based on the first and second knocksensor, and knock may be indicated in the first cylinder based on eitherthe first or the second knock sensor, while knock and pre-ignition isindicated in the second cylinder based on either the first or the secondknock sensor. During other conditions (conditions 25-32), pre-ignitionmay be indicated in the second cylinder based on the first and secondknock sensor, and knock may be indicated in the second cylinder based oneither the first or the second knock sensor, while knock andpre-ignition is indicated in the first cylinder based on either thefirst or the second knock sensor. In still another example, during someconditions (conditions 33-36), pre-ignition may be indicated in each ofthe first and second cylinder based on the first and second knocksensors, while knock is indicated in each of the first and the secondcylinder based on either the first or the second knock sensor.

During still other conditions, a plurality of knock-indicating sensorsand a plurality of pre-ignition-indicating sensors may be selected.Herein, at least one of the plurality of pre-ignition-indicating sensorsmay be the same as at least one of the plurality of knock-indicatingsensors (that is, at least one of the pre-ignition indicating sensorsmay overlap with at least one of the knock-indicating sensors). Forexample, during some conditions, the same plurality of knock sensors(that is, same set of sensors) may be used to identify knock andpre-ignition. Alternatively, each of the plurality ofpre-ignition-indicating sensors may be different from theknock-indicating sensor (that is, none of the pre-ignition indicatingsensors may overlap with any of the knock-indicating sensors).

Returning to the examples shown in table 600, during some conditions(conditions 41-44), knock may be indicated in the first cylinder basedon one of the first and second knock sensor, and pre-ignition may beindicated in the first cylinder based on each of the first and thesecond knock sensor, while knock is indicated in the second cylinderbased on each of the first and the second knock sensor, and pre-ignitionis indicated in the second cylinder based on one of the first and thesecond knock sensor. During other conditions (conditions 45-48), knockmay be indicated in the first cylinder based on each of the first andsecond knock sensor, and pre-ignition may be indicated in the firstcylinder based on one of the first and the second knock sensor, whileknock is indicated in the second cylinder based on one of the first andthe second knock sensor, and pre-ignition is indicated in the secondcylinder based on each of the first and the second knock sensor.

In another example, during some conditions (conditions 49-52), bothknock and pre-ignition may be indicated in the first cylinder based oneach of the first and second knock sensor, while each of knock andpre-ignition is indicated in the second cylinder based on one of thefirst and the second knock sensor. During other conditions (conditions53-56), both knock and pre-ignition may be indicated in the secondcylinder based on each of the first and second knock sensor, while eachof knock and pre-ignition is indicated in the first cylinder based onone of the first and the second knock sensor.

In another example, during some conditions (conditions 57-58), bothknock and pre-ignition may be indicated in the first cylinder based oneach of the first and second knock sensor, while knock is indicated inthe second cylinder based on each of the first and second knock sensorand pre-ignition is indicated in the second cylinder based on one of thefirst and the second knock sensor. During other conditions (conditions59-60), both knock and pre-ignition may be indicated in the firstcylinder based on each of the first and second knock sensor, while knockis indicated in the second cylinder based on one of the first and secondknock sensor and pre-ignition is indicated in the second cylinder basedon each of the first and the second knock sensor.

In the same way, during still other conditions (conditions 61-62), bothknock and pre-ignition may be indicated in the second cylinder based oneach of the first and second knock sensor, while knock is indicated inthe first cylinder based on one of the first and second knock sensor andpre-ignition is indicated in the first cylinder based on each of thefirst and the second knock sensor. During yet other conditions(conditions 63-64), both knock and pre-ignition may be indicated in thesecond cylinder based on each of the first and second knock sensor,while knock is indicated in the first cylinder based on each of thefirst and second knock sensor and pre-ignition is indicated in the firstcylinder based on one of the first and the second knock sensor.

In still further examples, each of knock and pre-ignition may beindicated in each of the first and the second cylinder based on aplurality of sensors. In the depicted example (condition 65), each ofknock and pre-ignition is indicated in each of the first and the secondcylinder based on the first and the second knock sensor. While thedepicted example illustrates using the same set of multiple sensors forindicating knock and pre-ignition in the different cylinders, it will beappreciated that in alternate examples, the selections may be partiallyoverlapping or non-overlapping. For example, in an engine that has fourknock sensors distributed along the engine block, during someconditions, knock may be indicated in each of the first and secondcylinder based on the first and second knock sensor while pre-ignitionis indicated in each of the first and second cylinder based on the thirdand fourth knock sensor. In another example, knock and pre-ignition maybe indicated in the first cylinder based on the first and second knocksensor while knock and pre-ignition is indicated in the second cylinderbased on the third and fourth knock sensor. Still further combinationsmay be possible.

It will be appreciated that while the examples depicted in table 600illustrate selecting a plurality of sensors for at least one of the twocylinders during some conditions, this is not meant to be limiting, andthat in further examples, two or more sensors may be selected from amonga plurality of sensors (e.g., from among three or more sensors). It willalso be appreciated that while the depicted examples illustrate sensorselections for two cylinders, the selection may be similarly made for aplurality of cylinders (that is, from cylinder 1 through cylinder n inan engine with n cylinders). In one example, the selections may bepre-mapped and stored in a look-up table (for example, in a speed-loadbased map) in the controller's memory.

In some examples, a knock-indicating sensor and apre-ignition-indicating sensor may be dynamically selected for each ofthe plurality of engine cylinders from among the plurality of knocksensors based on operating conditions, and further based on cylinderconfiguration. For example, in engines where engine cylinders arearranged as a group of cylinders (or bank of cylinders), a common sensor(or set of sensors) may be selected for indicating knock and/orpre-ignition for all cylinders on that bank. In one example, the look-uptable may have the selections pre-determined and stored in abank-specific manner. Herein, following the bank-specific detection,bank-specific mitigating actions may be taken, as described in detailherein.

In still further examples, the dynamic selection of sensors for knockand/or pre-ignition detection may be further adjusted based on thepre-ignition count, or history, of each cylinder. In one example, inresponse to persistent pre-ignition, the number of sensors used toidentify pre-ignition may be increased. For example, under a givenoperating condition, when the pre-ignition count of a cylinder is lowerthan a threshold count, a first or a second knock sensor may be used toindicate pre-ignition in the cylinder. In comparison, under the sameoperating condition, when the pre-ignition count of the cylinder ishigher than the threshold count, each of the first and second knocksensor (or more than two sensors) may be used to indicate pre-ignitionin the cylinder. Similarly, based on the pre-ignition count, thethresholds and/or windows for knock detection or pre-ignition detectionmay be adjusted. In one example, in response to a cylinder pre-ignitioncount being higher than a threshold (such as, when persistentpre-ignition is occurring in a cylinder), the pre-ignition detectionwindow may be broadened to start at an earlier timing, and/or end at alater timing. Additionally, the pre-ignition threshold may be lowered.By expanding the pre-ignition detection window and lowering thepre-ignition detection threshold, earlier occurrences of pre-ignitionmay be rapidly identified, and accordingly mitigating actions may betaken to reduce the persistence of pre-ignition.

Further still, the sensor selection may be adjusted based on the windowselection, and vice versa. In one example, broadening of a pre-ignitiondetection window due to an occurrence of persistent cylinderpre-ignition (or a cylinder pre-ignition count being higher than athreshold) may cause a previous selection of pre-ignition indicatingsensors to not suffice. Thus, in response to the broadening of thepre-ignition window, and based on the broadened window, the number andselection of knock-indicating and pre-ignition indicating sensors may beadjusted (e.g., increased). In one example, the engine controller may beconfigured to adaptively “learn” and accordingly update the look-uptable based on engine pre-ignition history and cylinder pre-ignitioncount.

In this way, during conditions when the output of any single knocksensor may not be sufficient to clearly and reliably identify anddifferentiate cylinder knock and cylinder pre-ignition, a plurality ofsensors may be used to better indicate and differentiate knock andpre-ignition in at least one engine cylinder.

Now turning to FIG. 7, graphs 700 and 750 show example outputs from afirst and a second knock sensor, respectively, the first and secondknock sensor positioned at distinct locations along an engine block.Based on the output of the sensors in each of a knock window and apre-ignition window, knock and pre-ignition may be determined anddifferentiated for each of a first and a second cylinder.

In the depicted example, based on the prevalent operating conditions,knock is indicated in the first cylinder based on an output of the firstknock sensor, while pre-ignition is indicated in the first cylinderbased on an output of the second knock sensor. Additionally, knock isindicated in the second cylinder based on the output of the second knocksensor, while pre-ignition is indicated in the second cylinder based onan output of the first knock sensor.

Graph 700 shows the output of the first knock sensor along the y-axis,as estimated at different crank angle degrees (CAD). A controller mayestimate the (first) output of the first knock sensor in a first crankangle window (window1 a) and indicate knock in the first cylinder basedon the first output as compared to a first knock threshold 701 in thefirst window. The controller may also estimate the (first) output of thefirst knock sensor in a second crank angle window (window2 a) andindicate pre-ignition in the second cylinder based on the first outputas compared to a second pre-ignition threshold 702 in the second window.In the depicted example, the first knock threshold 701 is lower than thesecond pre-ignition threshold 702. Also in the depicted example, thefirst crank angle window (window1 a) is a later window starting at CAD2and continuing to CAD4, while the second crank angle window (window2 a)is an earlier window starting at CAD1 and continuing to CAD3. That is,the first window partially overlaps with the second window (the overlapregion being between CAD2 and CAD3). In alternate examples, the firstand second windows may be fully overlapping (for example, a first windowbeing the same as the second window or a first, smaller window within asecond, larger window). Further still, the windows may be fully distinct(as shown below for the second knock sensor).

As shown in graph 700, in response to the output of the first knocksensor exceeding the first threshold 701 in the first window (window1a), knock may be indicated in the first cylinder. Also, in response tothe output of the first knock sensor exceeding the second threshold 702in the second window (window2 a), pre-ignition may be indicated in thesecond cylinder. in this way, by using a later window with a lowerthreshold for detecting knock while using an earlier window with ahigher threshold for detecting pre-ignition, earlier and more intenseabnormal combustion events related to pre-ignition may be betterdifferentiated from later and less intense abnormal combustion eventsrelated to knocking using the same knock sensor.

Graph 750 shows the output of the second knock sensor along the y-axis,as estimated at different crank angle degrees. A controller may estimatethe (second) output of the second knock sensor in a first crank anglewindow (window1 b) and indicate knock in the second cylinder based onthe second output as compared to a first knock threshold 751 in thefirst window. The controller may also estimate the (second) output ofthe second knock sensor in a second crank angle window (window2 b) andindicate pre-ignition in the first cylinder based on the second outputas compared to a second pre-ignition threshold 752 in the second window.In one example, the first knock threshold 751 may be lower than thesecond pre-ignition threshold 752. In the depicted example, the firstcrank angle window (window1 b) is a later window starting at CAD7 andcontinuing to CAD8, while the second crank angle window (window2 b) isan earlier window starting at CAD5 and continuing to CAD6. That is, thefirst window does not overlap with the second window.

As shown, in response to the output of the second knock sensor notexceeding the first threshold 751 in the first window (window1 b), knockmay not be determined in the second cylinder. Also, in response to theoutput of the second knock sensor not exceeding the second threshold 752in the second window (window 2 b), pre-ignition may not be determined inthe second cylinder.

While the depicted examples show distinct first and second windows forthe first and second sensors, it will be appreciated that in alternateexamples, the different sensors may have the same first and secondwindows. Similarly, while the depicted example shows distinct firstthresholds and distinct second thresholds for the first and secondsensors, in alternate examples, the different sensors may have the samethresholds in their first and second windows. As previously indicated,in still other examples, one or more of the sensors may have fullyoverlapping or partially overlapping first and second windows.

While the depicted example illustrates indicating knock and pre-ignitionbased on the output of the first or second knock sensor, it will beappreciated that in alternate examples, as indicated in FIGS. 5-6, knockand pre-ignition may be indicated based on the output of the first andthe second knock sensor. This may include, for example, indicating knockwhen a combined output of the first and second knock sensor in the first(later) window exceeds the first (lower) threshold, and indicatingpre-ignition when a combined output of the first and second knock sensorin the second (earlier) window exceeds the second (higher) threshold. Inanother example, this may include indicating knock when an output ofeach of the first and second knock sensor in the first window exceedsthe first threshold, and indicating pre-ignition when an output of eachof the first and second knock sensor in the second window exceeds thesecond threshold.

Following detection and differentiation, different control actions maybe taken to address knock and pre-ignition. For example, in response tothe indication of knock in the first cylinder, ignition spark timing ofthe first cylinder may be retarded away from MBT. In response to theindication of pre-ignition in the second cylinder, cylinder fuelinjection to the second cylinder may be enriched for a threshold numberof combustion events. The degree and/or duration of the cylinderenrichment may be adjusted based on the pre-ignition count (or history)of the second cylinder.

In some examples, the knock mitigation may be performed in acylinder-specific manner while the pre-ignition mitigation is performedin a bank-specific manner. For example, in response to the indication ofpre-ignition in the second cylinder, wherein the first and secondcylinders are arranged on a common bank (that is, in the same group ofcylinders), the controller may enrich cylinder fuel injection to thecommon bank for a predefined number of combustion events. In anotherexample, in response to an occurrence of pre-ignition in the secondcylinder, but not in the first cylinder, wherein the first cylinder ison a first bank (or first group of cylinders) and the second cylinder ison a second, different bank (or a second, different group of cylinders),the controller may enrich cylinder fuel injection of the second bankmore (e.g., higher degree of enrichment and/or longer duration) than thefirst bank.

In still another example, in response to an occurrence of pre-ignitionin the second cylinder and in the first cylinder, wherein the firstcylinder is on a first bank (or first group of cylinders) and the secondcylinder is on a second, different bank (or a second, different group ofcylinders), the controller may enrich fuel injection of the second bankbased on the pre-ignition count of the second cylinder while enrichingfuel injection of the first bank based on the pre-ignition count of thefirst cylinder. As such, enriching fuel injection of a bank based on thepre-ignition count of a cylinder may include increasing the degree ofenrichment and/or duration of enrichment (e.g., time, number ofcombustion events, etc.) of the bank as the pre-ignition count of theaffected cylinder increases. By enriching the pre-ignition affectedcylinder, the occurrence of further cylinder pre-ignition events isreduced.

In addition to enriching the pre-ignition affected cylinder (or bank), acam timing of the affected bank may be adjusted to limit an engine loadof the cylinder. Alternatively, in camless systems, one or more of acylinder port throttle, an electrically actuated intake valve and anelectrically actuated exhaust valve of the cylinder may be adjusted tolimit the load of the affected cylinder only. In either case, the loadlimiting may be increased as the cylinder pre-ignition count increases.By load-limiting the cylinder, the air-charge or air mass to thecylinder may be limited, thereby reducing the occurrence of furtherpre-ignition events.

In this way, by selecting one or more knock sensors, from among theavailable knock sensors, for indicating knock and pre-ignition in anengine cylinder, each of knock and pre-ignition may be more accuratelyidentified and differentiated from each other. By adjusting theselection for each cylinder, the detection may be improved for eachcylinder with the available sensors, and without necessitatingadditional sensors. By improving the performance and response-time ofpre-ignition detection, pre-ignition mitigation can be expedited,thereby reducing engine degradation due to pre-ignition.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method of operating an engine including afirst and a second knock sensor at different locations, comprising:during a first condition, indicating knock in a cylinder based on one ofthe first and second knock sensor while indicating pre-ignition in thecylinder based on each of the first and second knock sensor; and duringa second condition, indicating knock in the cylinder based on each ofthe first and second knock sensor while indicating pre-ignition in thecylinder based on one of the first and second knock sensor.
 2. Themethod of claim 1, wherein indicating knock based on one of the firstand second knock sensor includes indicating knock in a first cylinderbased on the first knock sensor and indicating knock in a secondcylinder based on the second knock sensor.
 3. The method of claim 1,wherein indicating knock based on one of the first and second knocksensor includes indicating knock in each of a first and a secondcylinder based on either the first knock sensor or the second knocksensor.
 4. The method of claim 1, wherein indicating pre-ignition basedon one of the first and second knock sensor includes indicatingpre-ignition in a first cylinder based on the first knock sensor andindicating pre-ignition in a second cylinder based on the second knocksensor.
 5. The method of claim 1, wherein indicating pre-ignition basedon one of the first and second knock sensor includes indicatingpre-ignition in each of a first and a second cylinder based on eitherthe first knock sensor or the second knock sensor.